The present invention relates to male fastener components that engage in openings of a female component, e.g. engage in openings of loops formed by fibers of a nonwoven female component. The invention more particularly relates to stem and head formations of the male elements that promote loop engageability and to methods and machines for their manufacture and their use.
There is a general need for male fastener components for hook and loop fasteners that provide good peel and shear strength properties in desired single or multiple directions and that are relatively inexpensive to manufacture. There is a specific need for low cost male fastener components that can function with low cost nonwoven loop materials.
There is also a need to be able to consistently and efficiently produce male fastener products having differing functional characteristics, using techniques that require limited changeover in basic tooling, yet allow for adjustments to produce the desired fastener characteristics.
Furthermore, it is especially desirable to extend the use of hook and loop fastening systems into fields of low cost products and still obtain good fastening performance. Examples include mid- and lowest-cost disposable diapers and sanitary products, disposable packaging for low price products, and disposable lowest cost surgical and industrial clothing and wraps, and single use medical and therapeutic devices. There are many other recognized low-cost product areas to which such fasteners would be applicable.
In particular it is desirable to obtain good engagement of the male member of the fastening systems with low cost nonwoven loop products that are characterized by their thinness and the low height to which their loop-defining fibers extend.
“Good engagement” in some instances means engaging a large percentage of hooks with low-lying loops. “Good engagement” in other applications often requires more, as in the case of fasteners for diapers, which require the hook component to exhibit strong “peel” resistance when engaged with thin, low cost loop materials. With such materials, the limited loop height does not permit significant transition of loading from the hook head to the hook stem during peeling action, as does occur with expensive loop products that have higher loop height. For this reason there are special problems to be addressed with hooks for thin loop structures in addition to the need to reduce the cost of the hook component and its tooling.
To explain the peel considerations more fully, in a hook and loop type fastener, “peel strength” is the resistance to stripping of one component from the other when a force normal to the mating surfaces is applied to the extremity of one of the components. Such peeling force on the component causes it to flex and progressively peel from the other. It is desirable to have peel strength in a hook and loop fastener that ensures that the closure does not release under normal forces of use but still permits the components to be separated when desired.
When the loop element is thin, as is usually the case for low-cost female fasteners, the individual loops are very short and low-lying. With application of a peel force, such loop exerts a force on the hook that is essentially perpendicular to the sheet-form base and parallel to the stem of the individual hooks. Consequently the force is applied primarily only to the heads of the hooks.
In contrast, when the loop element has a thick pile structure comprised of long individual loops, a loop must first be pulled out to its full length before it can exert significant force on a hook. As this occurs, the base webs to which the hooks and loops are attached are enabled to flex away from each other (see FIG. 1). Thus, at the point of separation of hooks from thick pile loops, the mated components are no longer face-to-face, and the angle at which a loop exerts its force on a hook is less than perpendicular. The longer the loop length, the more that angle diminishes. Thus, with a loop components having long loops, the force not only acts on the head of the hook, but also on its stem, and for very long loops, most of the resistance force is on the stem during peeling action.
However, for short loops, most of the resistance force is on the hook head, the consequence being that the hook head must be strong and provide much of the resistance to peel separation. Therefore, the use of thin and inexpensive loop components is to be expanded and improved, the hook head geometry must be improved to increase strength of engagement and produce an acceptable closure.
In many cases it is desirable to form the male hook members by molding an array of stems integrally (i.e. monolithically) with a common base, and subsequently post-treating the stems by a pressed formation step to form loop-engageable heads. In many instances it is desired to use continuous processes that act in a given machine direction, but to find a way to do this to achieve a hook product having good peel strength when the user applies peel forces at a substantial angle to the machine direction, in many cases at right angles, i.e. in the cross-machine direction.